Articles having electroless metal coatings incorporating wear-resisting particles therein

ABSTRACT

There are disclosed processes for electroless metallizing workpieces to provide thereon a metal coating incorporation therein non-metallic wear-resisting particles and the coated workpieces produced by such processes, the processes comprising contacting the workpieces with an electroless metallizing bath consisting of an aqueous solution of a metal salt and an electroless reducing agent therefor and a quantity of nonmetallic wear-resisting particles, wherein the particles are essentially insoluble in the plating bath and are non-catalytic and inert with respect thereto, the particles being present in the bath in an amount by weight no greater than about four times the weight of the metal in the bath expressed as free metal, and maintaining the particles in suspension throughout the bath during the metallizing of the workpiece; the electroless coating with the wear-resisting particles therein may be heat treated by heating to an elevated temperature in the range 100*C. to 600*C. for one hour or more further to harden the coating.

United States Patent [191 Metzger et a1.

[ ARTICLES HAVING ELECTROLESS METAL COATINGS INCORPORATING WEAR-RESISTING PARTICLES THEREIN [75] Inventors: Willy Metzger; Rudl Ott; Gunter Pappe; Helmut Schmidt, all of Solingen-Merscheid, Germany [73] Assignee: General American Transportation Corporation, Chicago, 111.

[22] Filed: Sept. 28, 1970 [21] App]. No.: 76,273

Related U.S. Application Data [62] Division of Ser. No. 698,127, Jan. 16, 1968, Pat. No.

[521 US. Cl. 29/195 [51] Int. Cl. 1332b 15/00 [58] Field of Search 29/195 M, 195 A,

[56] References Cited t UNITED STATES PATENTS 2,643,221 6/1953 Brenner et a1 204/43 P 3,061,525 10/1962 Grazen 204/9 2,775,531 12/1956 Montgomery et a1. 117/22 2,994,654 8/1961 Fahnoe et al 204/181 3,258,817 7/1966 Smiley 22/202 Aug. 21, 1973 Primary Examiner-L. Dewayne Rutledge Assistant Examiner-E L. Weise Attorney-Prangley, Clayton, Mullin, Dithmar and Vogel [5 7] ABSTRACT There are disclosed processes for electroless metallizing workpieces to provide thereon a metal coating incorporation therein non-metallic wear-resisting particles and the coated workpieces produced by such processes, the processes comprising contacting the workpieces with an electroless metallizing bath consisting of an aqueous solution of a metal salt and an electroless reducing agent therefor and a quantity of non-metallic wear-resisting particles, wherein the particles are essentially insoluble in the plating bath and are noncatalytic and inert with respect thereto, the particles being present in the bath in an amount by weight no greater than about four times the weight of the metal in the bath expressed as free metal, and maintaining the particles in suspension throughout the bath during the metallizing of the workpiece; the electroless coating with the wear-resisting particles therein may be heat treated by heating to an elevated temperature in the range 100C. to 600C. for one hour or more further to harden the coating.

23 Claims, No Drawings ARTICLES HAVING ELECTROLESS METAL COATINGS INCORPORATING WEAR-RESISTING PARTICLES TI-IEREIN This application is a division of copending application Ser. No. 698,129, filed Jan. 16, 1968 now US. Pat. No. 3,6l7,363 dated Nov. 2, 1971 for PROCESSES FOR ELECTROLESS METALLIZING INCORPO- RATING WEAR-RESISTING PARTICLES, AND THE PRODUCTS THEREOF.

The present invention is directed to workpieces carrying electroless metal coatings thereon wherein the metal coating has incorporated therein wear-resisting particles.

It is an important object of the present invention to provide an article of manufacture comprising a workpiece, a wear-resisting coating carried by the workpiece and formed of electroless metal having dispersed therethrough wear-resisting particles, the particles being essentially insoluble in aqueous solutions and being non-catalytic and inert with respect to electroless reducing agents for the electroless metal, the particles having dimensions on the order of from about 0.01 micron to about 100 microns and constituting by volume from about 1 to about 40 percent of the coating.

Another object of the present invention is to provide an article of manufacture of the type set forth in which the wear-resisting coating is electroless nickel and the particles dispersed therethrough have dimensions on the order of from about 0.5 microns to about 25 microns.

Still another object of the present invention is to provide an article of manufacture of the type set forth in which the wear-resisting coating is electroless cobalt and the wear-resisting particles dispersed therethrough have dimensions on the order of from about 0.5 microns to about 25 microns.

Still another object of the present invention is to provide an article of manufacture of the type set forth in which the wear-resisting coating is an alloy of electroless nickel and cobalt and the wear-resisting particles dis ersed ptherethrough have dimensions on the order 6 from about 0.5 ifiicronsto absurzsnteiaasi" A further object of the present invention is to provide an article of manufacture of the type set forth in which the wear-resisting coating is electroless copper and the wear-resisting particles dispersed therethrough have dimensions came order offfoin about 0.5 aiadns to about 25 microns.

A still further object of the present invention is to provide an article of manuafcture of the type set forth in which the wear-resisting coating has dispersed therethrough first wear-resisting particles and second wearresisting particles, the first wear-resisting particles having a hardness substantially greater than that of the electroless metal and the second wear-resisting parti-' cles imparting lubricating particles to the coating.

A still further object of the invention is to provide an article of manufacture comprising a workpiece having a wear-resistant coating thereon made in accordance with a process including the heat-hardening of the coating, wherein the metal is an electroless nickel that is an alloy containing from about 85 to about 97 percent nickel and from about 3 to percent phosphorus by weight and constituting a stable solid characterized by the presence of substantial micro-crystals of nickel phosphide dispersed in a matrix of nickel, or vice versa,

and having a resulting hardness within the approximate range 1,200 V.P.N. to 575 V.P.N.

Further features of the invention pertain to the particular workpieces, electroless metal coatings and wear-resistant particles dispersed therethrough,

whereby the above-outlined and additional operating I features thereof are attained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification and to the several illustrative examples set forth therein.

In accordance with the present invention, there is provided a workpiece or article of manufacture having an outer surface that is to carry the desired wearresistant coating, the outer surface typically being one that will be subject to sliding contact or rubbing contact with another surface, whereby to subject it to substantial wearing and bearing pressures. First, the workpiece is cleaned using one of several well-known cleaning methods, after which the workpiece is contacted with an electroless metallizing bath containing a quantity of wear-resisting particles, the bath being for example a conventional chemical nickel plating bath of the nickel cation-hypophosphite anion type, and the particles being essentially insoluble in the plating bath and non-catalytic and inert with respect thereto and being present in the bath in an amount by weight no greater than about four times the weight of the metal in the bath expressed as free metal. During the plating process, the wear-resisting particles are maintained in suspension throughout the bath, whereby after a suitable time interval there is produced on the surface of the workpiece coating of the metal, such as nickel, having uniformly dispersed therethrough a quantity of the wear-resisting particles. Thereafter the workpiece may be subjected to a heat-hardening step in order to render the composite coating thus produced intimately bonded thereto and of harder and more wear-resistant character.

The term wear-resistant coating" as used herein refers to a coating, the properties of which changed in any manner whatsoever to increase the wear-resistant properties thereof; for example, the term includes increasing the hardness of the coating by the incorporating therein materials that are intrinsically harder than the coating itself; on the other hand, the term as used herein may include coatings wherein a lubricating material, such as molybdenum disulfide, has been added to the coating so that the lubricated surface of the coating wears longer due to the lubricating properties thereof. Finally, it will be understood that the term wear-resistant coating" may also refer to a coating which embodies both particles which are intrinsically harder than the coating and particles which add a lubricating property to the coating.

While the processes for producing the articles of the present invention are fundamentally independent of the composition of the workpiece, ordinarily the workpiece is formed of an industrial metal such for example, as steel, although the workpiece may be formed of a non-metallic material. In the last mentioned instance, the workpiece is first subjected to pretreatment in order to activate the surface thereof so that it may subsequently receive the electroless metallized coating that is inherently produced in the metallizing process. When the metallizing metal is nickel, the pretreatment may be that as disclosed in U. S. Pat. No. 2,690,401, granted on Sept. 28, 1954 to Gregoire G'utzeit, William J. Crehan and Abraham Krieg, and in U. S. Pat. No. 2,690,402 granted on September 28, 1954 to William J. Crehan.

The process of the present application are particularly beneficial in providing wear-resistant coatings on workpieces formed of materials, such as aluminum, magnesium, copper, or beryllium which are not readily heat hardenable and which ordinarily are not heated after fabrication thereof, the inventive coated articles have wear-resistant properties such that additional treatment thereof is not necessary to provide a satisfactory wear-resistant surface.

It will be understood that a large number of metallizing processes of the electroless type may be utilized including electroless nickel processes, electroless cobalt processes and electroless copper processes. Of particular applicability to produce the articles of the present invention are electroless nickel processes, specifically those using hypophosphite anions as the electroless reducing agent. Furthermore, the electroless metallizing process in the case of electroless nickel is independent of the particular composition of the nickel plating bath of the nickel cation-hypophosphite anion type that is employed in the chemical nickel plating step, whereby a wide variety of these conventional chemical nickel plating baths may be employed; which plating baths inherently produce coatings essentially comprising by weight about 85 percent to 97 percent nickel and about 3 percent to percent phosphorus.

The plating bath disclosed in U. S. Pat. No. 2,822,294, granted on Feb. 4, 1958 to Gregoire Gutzeit, Paul Talmey and Warren G. Lee is particularly recommended due to its simplicity and economy. More particularly, this plating bath is of the nickel cationhypophosphite anion type, also containing lactic anion and propionic anion, and having a pH in the acid range 3.0 to 6.0. A typical example of this chemical nickel plating bath useful in the present invention has the following composition:

EXAMPLE 1 NiS0 .6H,0 0.08 mole/l NaH,PO,.H,O 0.23 mole/ 1 Lactic anion 0.30 mole/l Propionic anion 0.03 mole/l Lead ion 1 part per million pH 4.6

A quantity of the above plating bath was placed in a plating vessel having a magnetic stirrer therein, after which there was added thereto 1 percent by weight of the solids in the plating bath of 600 grit silicon carbide particles, it being noted that the nickel content of the bath on the solid basis expressed as nickel metal is about 0.5 percent. A steel workpiece having a bearing surface thereon was then placed in the plating bath while the silicon carbide particles were maintained in agitated suspension throughout the plating bath, and while the temperature of the plating bath was maintained in the general range 93C. to 98C. After about an hour, there was present on the exposed surfaces of the workpiece about one mil of a wear-resistant coating comprising electroless nickel and a quantity of the silicon carbide particles embedded in and distributed therethrough. The coating that is inherently produced by the particular plating bath essentially comprises by weight about 86 percent nickel and about 9% phosphorus, and about 5 percent silicon carbide.

The surface of the coated workpiece was rough and dull in appearance and had a hardness in the nickelphosphorus alloy area of 525 V.P.N. (Vickers Pyramid Number). The Taber Wear Index (TWl) was determined and was found to be 4.7. The Taber Wear index is defined as the loss of weight in mg. per 1000 revolutions of two CS-lO rubber wheels under a 1000 grams load, a TWll of 5 representing a loss in thickness of about 0.01 mil of coating. By contrast an electroless nickel coating made using the bath of Example 1 without the addition of wear-resisting particles thereto has a TWl of 15.2, whereby the article of the present invention having a coating incorporating therein the silicon carbide wear-resisting particles materially improves the wear-resistance of the coating, the improvement being essentially by a factor of 3.

1n the chemical nickel plating bath of Example 1, the absolute concentration of hypophosphite in the bath expressed in mole/liter may vary within the range from about 0.15 to about 1.20, and the ratio between the nickel cations and hypophosphite anions in the bath expressed in molar concentrations may vary within the range from about 0.25 to about 1.60. The lactic anion serves as a complexing agent and may be derived from lactic acid or salts thereof, the absolute concentration of lactic ions in the bath expressed in mole/liter being within the range from about 0.25 to about 0.60. The bath also includes an exalting additive, namely, the propionic anion, which has a concentration in the bath expressed in mole/liter in the range from about 0.025 to about 0.060. Other exalting additives may be used in place of the propionic anion, the exalting additive being selected from the group consisting of simple short chain saturated aliphatic monocarboxylic acids, including three to five carbon atoms and salts thereof. Further details of the composition of the bath and the method of using the same are set forth in the aforementioned U. S. Pat. No. 2,822,294 and the disclosure thereof is incorporated herein by reference.

The silicon carbide particles useful in the process of Example 1 may have a particle size in the range from about 0.5 micron to about 25 microns, in order to obtain good suspension of the particles in the plating bath and in order to obtain uniform distribution of the particles in coating. Smaller particles inhibit the plating action, due to close packing, while larger particles are kept dispersed in the plating bath only with extreme difficulty. The concentration of the silicon carbon carbide particles in the plating bath should not exceed about four times the weight of the nickel metal present in the bath expressed as free metal, although smaller concentration of the silicon carbide particles may be utilized, it being understood that the volume of silicon carbide in the coating will be a function of the concentration of the silicon carbide particles in the plating bath as well as the effectiveness of the dispersion thereof. in Example 1, the silicon carbide comprises about 15 percent by volume of the wear-resistant coating, although it will be understood that the volume of the silicon carbide particles may vary from as little as 1 percent up to as much as 40 percent of the volume of the coating.

Other thicknesses of the coating may be provided, and the coating may have a thickness in the range from about 5 microns to about 200 microns or more if desired.

Summarizing, with respect to Example 1 above, there is provided a process of electroless plating of a nick el-phosphorus alloy coating on a workpiece, the coating containing silicon carbide particles distributed therethrough and being a relatively thick dispersion hardened" metal deposit. The expression electroless plating as used herein refers to the plating of metal coatings without the application of an external electrical current, and preferably by a chemical reduction of the electroless metal utilizing an electroless reducing agent for the metal, thereby to accomplish a process of electroless metallizing. The term dispersion hardened as used herein refers to the described metal coatings in which are embedded inert solid particles during the laying down of the metal coating, the particles being partially or completely embedded in and held in position by the coating.

The lead content of the nickel plating bath of Example 1 performs the important function of stabilizing the bath during the plating operation. It will be understood that other types of stabilizers and other amounts of stabilizers may be advantageously utilized in connection with the present invention, suitable such stabilizers being disclosed in U. S. Pat. No. 2,762,723 granted Sept. 11, 1956 to Paul Talmey and Gregoire Gutzeit, the disclosure of that patent being incorporated herein by reference.

Alkaline nickel plating baths may be utilized advantageously in the present invention, and particularly when coating certain plastics and certain metals such as magnesium, examples of suitable alkaline baths being set forth in U. S. Pat. No. 3,21 1,578 granted Oct. 12, 1965 to Gregoire Gutzeit, the disclosure thereof being incorporated herein by reference.

In general any non-metallic particle may be utilized as a wear-resisting particle in the process of Example 1, it simply being necessary that the particles be essentially insoluble in the plating bath and that the particles be non-catalytic and inert with respect to the reducing of the metal salt by the electroless reducing agent therefor. In this connection it pointed out that a wide variety of such non-metallic wear-resisting particles may be used, and more specifically, there may be used the following: kaolin; glass flour, talc, synthetic organic plastic resin powders; and oxides, carbides, nitrides, borides, silicides, sulfides, silicates, sulfates, carbonates, phosphates, oxalates or fluorides of aluminum, boron, chromium, hafnium, molybdenum, silicon, titanium, tantalum, vanadium, tungsten, zirconium, nickel, magnesium calcium, barium, strontium, cerium, iron or manganese. The particle size of the wear-resisting particles may be of the order of 0.01 micron to 100 microns, a preferred size being in the range from about 0.5 micron to about 25 microns.

Furthermore, the particles must be essentially insoluble in the plating bath, i.e., must have a very low solubility therein on the order of no more than about 0.01 mole per liter. In addition, the wear-resisting particles must be non-catalytic and inert with respect to the reducing agent and the reaction of the reducing agent with the coating metal in the bath, and also the particles must not interfere with or stop the plating reaction. The concentration of the wear-resisting particles in the plating bath is preferably in the range from about 0.1 percent by weight of the solids to about 2 percent by weight of the solids, but in any event not more than four times the weight of the electroless plating metal in the bath when the weight of the metal is expressed as the free or reduced metal. In certain instances it may be desirable to provide an acid or solvent wash to the particles before the addition thereof to the plating bath, thereby to avoid contamination and to increase the stability of the plating bath.

Other suitable methods of maintaining the wear resisting particles in suspension may be used in addition to that described above with respect to Example 1. For example, a mixture of the plating solution and the wear-resisting particles may be advantageously pumped through the bottom of the plating vessel, the bottom of the plating vessel being dish-shaped and symmetrical, whereby a uniform stream of the plating bath with the wear-resisting particle suspended and entrained therein is passed or flooded across the surfaces of the workpiece being coated.

Another advantageous system for maintaining the wear-resisting particles in suspension is to provide a symmetrical plating bath having dispersed in the bottom thereof a spider including a number of very small gas outlets therein. in this manner very fine air bubbles can be introduced into the plating bath via the spider, the air bubbles serving to hold the wear-resisting particles in suspension throughout the plating solution. Other gases such as nitrogen, or one of the noble gases, may be used in place of air.

Yet another method of maintaining the wearresisting particles in suspension is to agitate and move the workpiece within the plating solution, such movement of the workpiece causing currents in the plating solution which tend to hold the wear-resisting particles in suspension. Each of the above-mentioned alternative methods of maintaining the wear-resisting particles in suspension has been successfully utilized in conjunction with the process of Example 1 above.

it will be appreciated that the process of Example 1 is particularly useful when applied to workpieces having surfaces that are to be employed in sliding applications, such as slide bearings, motor housings, shafts, and the like. it will be understood, however, that the incorporation of the wear-resisting particles in the electroless deposited metal coating affects other properties of the coating in addition to the hardness and wearresistance thereof. In general the physical, chemical and electrochemical properties of the coating are affected including the coefficient of friction, the temperature stability of the coating, the oxidation stability of the coating, the corrosion stability of the coating, the reflectivity and/or gloss thereof, etc.

Turning now to a consideration of the electroless chemical nickel plating baths useful in producing the' EXAMPLE 2 Nickel chloride Sodium acetate 30 gm/l. l3 gm/l.

Sodium hypophosphite l gm/l. H 4

"l'emperature 95C.

A plating bath as set forth above was placed in a symmetrical plating vessel and there was added 240 grit silicon carbide particles in an amount equal to 2 percent of the solids in the plating bath. After an hour of plating, a rough dull coating having a thickness of 0.65 mil was provided on a workpiece disposed therein, the plating solution being continuously agitated by stirring to hold the silicon carbide particles in suspension therein. The resultant coating had the valuable properties as set forth both with respect to the coating of Example 1.

EXAMPLE 3 Nickel sulfate 30 gmll. Sodium citrate 100 gmll. Ammonium chloride 50 gm/l Sodium hypophosphite l0 gmll. pH 8-l0 Temperature 95C.

The plating process of Example 1 was repeated utilizing the bath of the above composition, there being produced on the workpiece an electroless nickel coating having the silicon carbide particles uniformly dispersed therethrough, the coating possessing the valuable properties described with respect to Example 1.

The hardness of the electroless nickel coatings incorporating therein the silicon carbide particles as described in conjunction with Examples 1 to 3 above can be further hardened and rendered even more wearresistant by a heat treatment of the coating after deposition thereof. There is disclosed in U. S. Pat. No. 2,908,419, granted on Oct. 13, 1959 to Paul Talmey and William J. Crehan a suitable heat treatment process to increase the hardness of such electroless nickel coatings, and the disclosure of that patent is incorporated herein by reference. The electroless nickel portion of the coatings of Examples 1 to 3 may contain from about 85% to about 97% nickel and from about 3 percent to about percent phosphorus by weight, certain of the baths such as that of Example 1 actually providing compositions in the range from 88 percent to 94 percent nickel and from about 6 percent to about 12 percent phosphorus by weight. The electroless nickel coating more specifically after heat treatment constitutes a stable solid characterized by the presence of substantial microcrystals of nickel dispersed in a matrix of nickel phosphide and having a resultant hardness as high as 1200 V.P.N. the hardness varying down to about 575 V.P.N. depending upon the heating temperature and time.

The following is an example of the heat treatment of the novel coated article of Example 1.

EXAMPLE 4 A workpiece having a coating thereon produced as in Example 1 was gradually heated in an oven from 100C. to 400C. for a period of one hour. At the end of the hour it was found that the hardness of the electroless nickel portion of the coating was 1,081 V.P.N. and the wear-resistances was 1.9 TWI. This compared with a TWl of 4.2 for the electroless nickel coating alone without the addition of the wear-resisting particles thereto.

It will be appreciated that the coatings of Examples 2 and 3 above can be likwise heat-hardened by processing in accordance with Example 4 herein, and further as explained in the U. 5. Pat. No. 2,908,419 referred to above.

It has been found that sulfides are also useful as wearresisting particles in the present invention, the following being examples of the use of molybdenum sulfide particles as the wear-resisting particles.

EXAMPLE 5 The plating bath and the coating process of Example lwere duplicated but the plating bath had disposed therein 1 percent by weight of the dry solids of granulated molybdenum disulfide having an average particle size of about 50 microns. There resulted from one hour of plating a coating having a thickness of 0.78 mil and possessing a rough texture. The hardness of the electroless nickel coating was 508 V.P.N. and the wearresistance thereof was 4.9 TWI. The coated workpiece made in accordance with Example 5 had good lubricating properties imparted thereto by the molybdenum disulfide and possessed the other advantages and properties as described above with respect to Example 4.

The coating of Example 5 may also be heathardened, an example of such a process being as follows:

EXAMPLE 6 A workpiece with the coating of Example 5 thereon with further processed and heat treated as in Example 4 above to provide a heat-hardened coating having a hardness of 1018 V.P.N. and a wear resistance of 1.1 TWI.

Metal oxides are examples of other wear-resisting particles which are useful in carrying out the processes of the present invention. The following is an example utilizing aluminum oxide particles:

EXAMPLE 7 The plating bath and process of Example 1 was utilized but there was substituted for the silicon carbide particles aluminum oxide particles having a size of about 0.5 micron, and having a concentration by weight of about 1 percent of the dry solids in the plating bath. There was produced a bright coating of electroless nickel having dispersed therethrough the aluminum oxide particles, 0.6 mil of the coating being produced in one hours time. The hardness of the coating in the nickel area was 572 V.P.M. and the wearresistance thereof was 9.8 TWI. The wear-resistant coating made in accordance with Example 7 had the other desirable properties of the coating produced by the process of Example 1 as set forth above.

The process of Example 7 was repeated utilizing a concentration of the aluminum oxide particles of 0.1 percent by weight on a dry basis of the solids in the plating bath. There resulted after one hour of plating a coating having a thickness of 0.6 mil and a hardness of 627 V.P.N. in another process in accordance with Example 7, the aluminum oxide particles were present in the plating bath in a concentration of 2 percent by weight on a dry basis of the solids, there resulting a rough coating having a thickness of 0.43 mil and a hardness of 642 V.P.N. in yet another variation of the process of Example 7, the aluminum oxide particles utilized had a size of 0.05 micron and a concentration of 1 percent in the bath, thereby to produce after one hour a bright coating having a thickness of 0.67 mil and a hardness of 612 V.P.N.

Finally, there was carried out a variation of the process of Example 7, wherein the aluminum oxide particles had a size of 1 micron and were present in a concentration of l percent in the bath, there resulting after one hour of plating a rough coating having a thickness EXAMPLE 8 A workpiece coated in accordance with the process of Example 7 was heat-treated in accordance with the process of Example 4, the resultant coating having a hardness of 1049 V.P.N. and a wear-resistance of 4.6 TWI.

A wide variety of metal oxides may be utilized in the place of aluminum oxide in Examples 7 and 8, and more specifically, titanium oxides may be utilized to provide a dull rough coating having a thickness of 0.54 mil after one hour of plating and a hardness of 572 V.P.N. Tin oxide powder substituted for the aluminum oxide in Example 7 provided after one hour a bright coating having a thickness of 0.59 mil and a hardness of 536 V.P.N. While chromium oxide when substituted in Example 7 in the form of a liquid containing particles of 0.5 micron size after one hour produced a dull smooth coating having a thickness of 0.69 mil and .a hardness of 525 V.P.N.

Silicas having a small particle size comprise another class of materials that are particularly useful as wearresisting particles in the processes of the present invention, examples of which are as follows:

EXAMPLE 9 The process of Example 1 was repeated using the bath thereof but substituting silica as the wear-resisting particles therein, the silica utilized being that sold under the trade designation Syloid 244" and having a particle size in range l-S microns. After one hour of plating with a 1 percent concentration of the silica in the bath on a dry weight basis, there was produced a bright coating having a thickness of 0.76 mil, a hardness of 525 V.P.N. and a wear-resistance of 14.6 TWl. Comparable results were obtained utilizing other synthetic silicas including that sold under the trade designation Syloid 266" and that sold under the trade designation QUSO 6-30.

The coating of Example 10 can be further hardened by heat treatment thereof and the following is an example:

EXAMPLE 10 A workpiece carrying a coating made in accordance with Example 9 was heat treated in accordance with Example 4, and there resulted a coating having a hardness of 1064 V.P.N. and a wear-resistance of 6 TW].

The processes herein disclosed are is also particularly useful in applying wear-resistant coatings to aluminum castings and forgings which cannot be heat-hardened, but which have surfaces that must be wear-resistant. The following is an example of the application of a wear-resistant coating to an aluminum workpiece:

EXAMPLE 1] The plating bath of Example 1 was modified by adding thereto 0.5 grams per liter of potassium fluoride dihydrate,the preferred concentration being in the range from about 0.001 to about 0.04 mol/liter. An aluminum workpiece was then coated in accordance with the process of Example 1 to provide thereon a rough dull coating having a thickness after one hour of plating of 0.54 mil, a hardness of 508 V.P.N. and a wear-resistance of 4.5 TWI. It will be appreciated that this workpiece has a bearing surface provided by the coating that is materially more wear-resistant than either the aluminum metal or the electroless nickel plate without the addi' tion of the silicon carbide particles thereto.

in certain instances, it is possible to heat treat aluminum base workpieces, the following being an example of such a heat treatment:

EXAMPLE 12 The aluminum workpiece of Example 11 was heated to C. for one hour to provide a heat-hardening of the coating thereon. More specifically, the coating now had a hardness of 724 V.P.N. and a wear-resistance of 3.2 even after this mild heat treatment of the workpiece.

As noted above, the workpiece of Examples 11 and 12 are rough and dull in appearance. It has been found that if the surface of the coating of Example ll, i.e., without heat-treatment, is honedl or lapped to render the surface smooth, the wear-resistance thereof is improved and more specifically the TWI is decreased to about 2.2.

Other carbides are useful as wear-resisting particles when applied to aluminum base workpieces, the following being an example thereof:

EXAMPLE 13 The process of Example ll was repeated, but there was substituted for the silicon carbide particles therein tungsten carbide particles having a size of 400 mesh maximum, the tungsten carbide being that sold under the trade designation Haynes Alloy No. 956". The tungsten carbide particles were utilized in .a concentration of 1 percent of the dry solids in the bath, and after one hour of plating, there was provided a rough coating having a thickness of 0.45 mil, a hardness of 593 V.P.N., and a wear-resistance of 6.6 TWl.

The coating of Example 13 can also be further hardened by heat treatment thereof, the following being an example:

EXAMPLE l4 The aluminum workpiece with the coating of Example l3 thereon was heat treated by being heated to a temperature of 270C. for 16 hours. The heat treated coating was found to have a hardness of 1145 V.P.N. and a wear-resistance of 2.1 TWI.

Certain metal sulfides may also advantageously be incorporated in electroless nickel plating applied to aluminum base alloys, the following being an example thereof:

EXAMPLE l5 The process of Example 5 was repeated by substituting an aluminum base workpiece for the steel workpiece thereof, whereby there was provided after one hour of plating a rough coating having a thickness of 0.78 mil, a hardness of 606 V.P.N. and a wearresistance of 2.7.

The workpiece of Example 15 if heat treated can have the hardness of the coating thereon increased, the following being an example:

EXAMPLE 16 EXAMPLE 17 There was provided an electroless nickel plating bath having the following composition and characteristics:

Nickel chloride Sodium citrate Sodium acetate Sodium succinate N-diethylborazane Lead chloride Methanol pH 6 Temperature 65C.

30 gm/l l0 gm/l gm/l A quantity of silicon carbide particles was added to the above plating bath with a concentration of l percent of the dry ingredients in the bath, the silicon carbide having a size of grit 600. A steel workpiece was immersed in the plating both and the particles were held in suspension by stirring of the bath. After one hour there was provided a coating of electroless coating on the workpiece, the coating having dispersed therein silicon carbide particles. The coating had all of the useful characteristics and advantages described above with respect to the coating produced by the process of Example I.

Other borazane reducing agents may be used in place of that set forth in Example 17 above. in general, an alkyl-borazane may be used, another preferred reducing agent being dimethyl-borazane. Also useful is sodium borahydride.

The present invention is also applicable to processes wherein other metals are plated by electroless plating, the following being examples of the plating of cobalt coatings on steel workpieces and incorporating in the coatings wear-resisting particles, all in accordance with the present invention.

EXAMPLE 18 There was formulated an electroless cobalt plating solution having the following composition and characteristics:

Cobalt chloride Sodium acetate Sodium hypophosphite emperature There was added to this solution 1% by weight of the dry ingredients thereof of silicon carbon particles having the size of 600 grit. After one hour of plating during which the solution was thoroughly agitated uniformly to suspend the silicon carbide particles, there was produced on the surface of the workpiecean electroless cobalt coating having uniformly dispersed therethrough silicon carbide particles. The resultant coating had the desirable characteristics described above with respect to the coating produced by the process of Example 1.

EXAMPLE 19 A plating solution having the following composition and characteristics was formulated:

Cobalt sulfate 30 gm/l Sodium citrate l 10 gm/l Ammonium chloride 45 gm/l Sodium hypophosphite l2 grn/l pH 9 Temperature C.

There was added to the plating solution silicon carbide particles in a concentration of 1% of the dry ingredients of this plating solution, the particles having the size of 600 grit. A steel workpiece was placed in the plating solution and the solution was vigorously stirred to suspend the silicon carbide particles uniformly therethrough; after an hour, there was produced on the surface of the workpiece a coating of electroless cobalt having a silicon carbide particles uniformly dispersed therethrough. The coating had all of the desirable characteristics and advantages of the coating of the process of Example 1, described above.

Two electroless metals may be co-deposited from an electroless plating solution as is known in the art and such plating solutions are useful in carrying out the process of the present invention, the following being examples thereofz EXAMPLE 20 An electroless plating solution was fonnulated having the following composition and characteristics:

Nickel chloride 20 gm/l Cobalt chloride 10 gm/l Sodium citrate 20 gm/l Sodium hypophosphite l0 gm/l P" 4.2 Temperature 95C.

To the plating solution there was added silicon carbide particles in a concentration of 1 percent of the dry ingredients by weight, the particles having the size of 600 grit. A steel workpiece was immersed in the plating solution while the plating solution was vigorously stirred so as uniformly to suspend the silicon carbide particles throughout the volume thereof. After an hour of plating, there was provided on the workpiece a nickel-cobalt coating having uniformly dispersed therethrough silicon carbide particles. The resultant coating had the several desirable properties and characteristics discussed above with respect to the coating produced by the process of Example 1.

EXAMPLE 21 An electroless plating solution was formulated having the following composition and characteristics:

Nickel sulfate 25 gmll Cobalt chloride 5 gm/l Ammonium chloride 60 gm/l Sadium hypophosphite l5 gm/l 9.5 Temperature 95C.

To this plating solution was added silicon carbide particles in a concentration of 1 percent by weight of the dry ingredients therein, the particles having a size of 600 grit. A steel workpiece was immersed in the plating solution while the solution was vigorously agitated to maintain the silicon carbide particles in suspension throughout the solution during the coating of the workpiece. After an hour, the workpiece had thereon a nickel-cobalt having silicon carbide particles uniformly dispersed therethrough. The coating was wear-resistant and had the desirable properties and characteristics discussed above with respect to the coating produced by the process of Example 1.

It will be understood that the hardness and wearresistance of the coatings of Examples 17 through 21 can be improved by heat treatment thereof, i.e., by the heating thereof to an elevated temperature for a sufficient period of time to effect a heat-hardening thereof.

The following is an example of yet another electroless metal and an electroless plating solution useful in carrying out the present invention:

EXAMPLE 22 An electroless plating bath was formulated having the following composition and characteristics:

Copper sulfate gm/l Triethanolamine 100 gm/l Formaldehyde solution 20 ml/l pH 12.5 Temperature C.

There was added to the electroless plating solution silicon carbide particles in a concentration of 1 percent by weight of the dry ingredients in the solution, the silicon carbide particles having a size of 600 grit. A steel workpiece was immersed in the plating solution and the solution was vigorously agitated to maintain the silicon carbide particles in suspension throughout the solution during the coating of the workpiece. After an hour, the workpiece had an appreciable coating thereon of copper having dispersed uniformly therethrough silicon carbide particles. The resultant coating had the hardness and wear-resistance and other desirable properties and characteristics discussed above with respect to the coating provided by the process of Example 1.

The following are yet other examples of workpieces which may be successfully coated utilizing the present invention, the chemical composition being other than the steel and aluminum given in the above specific examples.

EXAMPLE 23 The process of Example 1 was repeated using a workpiece consisting of copper with essentially the same results in regard to the wear-resistance of the coating obtained.

EXAMPLE 24 The process of Example 1 was repeated using a workpiece consisting of brass with essentially the same results in regard to the wear-resistance of the coating obtained.

EXAMPLE 25 The process of Example 1 was repeated using a workpiece consisting of beryllium alloy with essentially the same results in regard to the wear-resistance of the coating obtained.

EXAMPLE 26 The process of Example 1 was repeated using a work- 7 piece consisting of nickel with essentially the same resultsin regard to the wear-resistance of the coatingobtained.

EXAMPLE 27 The process of Example 17 was repeated using a workpiece of magnesium. The coating had allof the characteristics described above with respect to the wear-resistance of the coating of Example 17.

Yet other wear-resisting particlesmay be utilized advantageously inthe present invention as follows:

EXAMPLE 28 The electroless plating bath of Example 1 was utilized in the process of Example 1, but 1 percent by weight onthe dry basis of boron nitride was substituted for the silicon carbide therein. The coating obtained after one .hour of plating had much improved wearresistance due fundamentally to the lubricating properties of the boron nitride particles.

EXAMPLE 29 The plating solution and the process of Example 1 were repeated but there was substituted for the silicon carbide therein 1 percent by weight of Microthene FN-SlO, a polyethylene resin powder having a particle size in the range less than 30 microns. There was obtained an electroless metal coating which had improved wear-resistance due to the incorporation of the plastic particles therein.

It will be understood that the weanresisting properties of the coatings made in accordance with the pres ent invention may be derived from both the incorporation of hard particles therein and the incorporationof lubricatingparticles therein. The following is an example of such a process and coating derived therefrom.

EXAMPLE 30 The plating bath and the process of Example 1 were utilized but there was in addition added thereto 1 percent by weight on a dry basis of molybdenum disulfide having a particle size of about 50 microns. The resultant coating had much improved wear-resistance, the wear-resistance being imparted thereto both by the hard silicon carbide particles and the lubricating molybdenum disulfide particles.

From the above, it will be seen that therehave been provided processes for electroless metallizing of workpieces to provide thereon metal coatings incorporating therein wear-resisting particles, which coated workpieces fulfill all of the objects and advantages set forth above.

While there have been described what are at present considered to be certain preferred embodiments of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An article of manufacture comprising a workpiece,

.a wear-resistant coating carried by said workpiece and formed of an electroless metal alloy consisting of an electroless metal selected from the class consisting of nickel, cobalt and copper and an element selected from the class consisting of phosphorus and boron, said electroless metal alloy containing from about 85 percent to about 97 percent of the electroless metal and from about 3 percent to about 15 percent of the element by weight and having disbursed therethrough wearresisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order of from 0.01 micron to about 100 microns and consisting by volume from about l percent to about 40 percent of said coating.

2. The article of manufacture set forth in claim 1, wherein said wear-resisting particles are silicon carbide particles.

3. An article of manufacture set forth in claim 1, wherein said wear-resisting particles are tungsten carbide particles.

4. The article of manufacture set forth in claim 1, wherein said wear-resisting particles are molybdenum sulfide particles.

5. The article of manufacture set forth in claim I, wherein said wear-resisting particles are silica particles.

6. The article of manufacture set forth in claim 1, wherein said wear-resisting particles are aluminum oxide particles.

7. The article of manufacture set forth in claim 1, wherein said wear-resisting particles have dimensions in the range from about 0.5 micron to about 25 microns.

8. The article of manufacture set forth in claim 1, wherein said layer has a thickness in the range from about 5 microns to about 200 microns.

9. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from iron and the alloys thereof.

10. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from nickel and the alloys thereof.

11. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from aluminum and the alloys thereof.

12. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from magnesium and the alloys thereof.

13. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from beryllium and the alloys thereof.

14. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from copper and the alloys thereof.

15. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless nickel alloy consisting of nickel and an element selected from the class consisting of phosphorus and boron, said electroless nickel alloy containing from about 85 percent to about 97 percent nickel and from about 3 percent to about percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order from about 0.5 micron to about 25 microns and consisting by volume from about 1 percent to about 40 percent of said coating.

16. The article of manufacture set forth in claim 15, wherein said electroless nickel is an alloy containing from about percent to 97 percent nickel and from about 3 percent to 15 percent phosphorous by weight and constituting a stable solid characterized by the presence of substantial microcrystals of nickel dispersed in a matrix of nickel phosphide and having a resulting hardness within the approximate range 1200 V.P.N. and 575 V.P.N.

17. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless cobalt alloy consisting of cobalt and an element selected from the class consisting of phosphorus and boron, said electroless cobalt alloy containing from about 85 percent to about 97 percent cobalt and from about 3 percent to about l5 percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.

18. An article of manufacture comprising a work piece, a wear-resistant coating carried by said workpiece and formed of an alloy of electroless nickel and cobalt and an element selected from the class consisting of phosphorus and boron, said alloy consisting of from about 85 percent to about 97 percent of the metal and from about 3 percent to about 15 percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being noncatalytic and inert with respect thereto, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.

19. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless copper alloy consisting of an element selected from the class consisting of phosphorus and boron, said electroless copper alloy consisting of from about 85 percent to about 97 percent copper and from about 3 percent to about l5 percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.

20. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless metal alloy consisting of an electroless metal selected from the class consisting of nickel, cobalt, alloys of nickel and cobalt and copper and an element selected from the class consisting of phosphorus and boron, said alloy consisting of from about 85 percent to about 97 percent of the metal and from about 3 percent to about 15 percent of the element by weight and having dispersed therethrough first wear-resisting particles and second wear-resisting particles, all of said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said first wear-resisting particles having a hardness substantially greater than that of said electroless metal alloy, said second wear-resisting particles imparting lubricating properties to said coating, all of said particles having dimensions on the order of from about 0.01 micron to about microns and constituting by volume from about 1 percent to about 40 percent of said coating. 7

21. An article of manufacture set forth in claim 20, wherein said first wear-resisting particles are silicon carbide particles and said second wear-resisting particles are molybdenum disulfide particles.

22. An article of manufacturing comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of electroless nickel alloy containing from about 85 percent to 97 percent nickel and from about 3 to about percent phosphorus by weight, said coating having disbursed there through wear-resisting particles, said particles being essentially insoluble in aqueous solutions and being non-catalytic and inert with respect to the electroless reducing agents for nickel, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.

23. An article of manufacturing comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of electroless nickel alloy containing from about percent to 97 percent nickel and from about 3 percent to 15 percent phosphorus by weight and constituting a stable solid characterized by the presence of substantial micro-crystals of nickel phosphide dispersed in a matrix of nickel and having a resulting hardness within the approximate range l200V.P.N. to 575V.P.N., said wearresistant coating having a disbursed therethrough wear-resistant particles, said particles being essentially insoluble in aqueous solutions and being non-catalytic and inert with respect to the electroless reducing agents for nickel, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.

A UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,753,667 I Dated August 21. 1973 In vent r( Willy Metzger et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 15, column 15, line 64, "consisting" should bo I --constituting--;

cloimzo, column 17, line 4, "10" should be --100--;

Claim 22, column 17, line 15 after 3 insert --percent--; and

Signed and sealed this 8th day of Jnuar'y l97li.

(SEAL) Attest: I

EDWARD M.FLETCHER,JR. D. TEGTMEYER Attesting Officer Acting Commissioner of Patents FORM PO-IQSO (10-69) USCOMM-DC 60376-1 69 us, sovnrmsm' PRINTING pmcs: I959 o-ass-za4 DZ 

2. The article of manufacture set forth in claim 1, wherein said wear-resisting particles are silicon carbide particles.
 3. An article of manufacture set forth in claim 1, wherein said wear-resisting particles are tungsten carbide particles.
 4. The article of manufacture set forth in claim 1, wherein said wear-resisting particles are molybdenum sulfide particles.
 5. The article of manufacture set forth in claim 1, wherein said wear-resisting particles are silica particles.
 6. The article of manufacture set forth in claim 1, wherein said wear-resisting particles are aluminum oxide particles.
 7. The article of manufacture set forth in claim 1, wherein said wear-resisting particles have dimensions in the range from about 0.5 micron to about 25 microns.
 8. The article of manufacture set forth in claim 1, wherein said layer has a thickness in the range from about 5 microns to about 200 microns.
 9. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from iron and the alloys thereof.
 10. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from nickel and the alloys thereof.
 11. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from aluminum and the alloys thereof.
 12. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from magnesium and the alloys thereof.
 13. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from beryllium and the alloys thereof.
 14. The article of manufacture set forth in claim 1, wherein said workpiece is formed of a metal selected from copper and the alloys thereof.
 15. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless nickel alloy consisting of nickel and an element selected from the class consisting of phosphorus and boron, said electroless nickel alloy containing from about 85 percent to about 97 percent nickel and from about 3 percent to about 15 percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order from about 0.5 micron to about 25 microns and consisting by volume from about 1 percent to about 40 percent of said coating.
 16. The article of manufacture set forth in claim 15, wherein said electroless nickel is an alloy containing from about 85 percent to 97 percent nickel and from about 3 percent to 15 percent phosphorous by weight and constituting a stable solid characterized by the presence of substantial microcrystals of nickel dispersed in a matrix of nickel phosphide and having a resulting hardness within the approximate range 1200 V.P.N. and 575 V.P.N.
 17. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless cobalt alloy consisting of cobalt and an element selected from the class consisting of phosphorus and boron, said electroless cobalt alloy containing from about 85 percent to about 97 percent cobalt and from about 3 percent to about 15 percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.
 18. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an alloy of electroless nickel and cobalt and an element selected from the class consisting of phosphorus and boron, said alloy consisting of from about 85 percent to about 97 percent of the metal and from about 3 percent to about 15 percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.
 19. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless copper alloy consisting of an element selected from the class consisting of phosphorus and boron, said electroless copper alloy consisting of from about 85 percent to about 97 percent copper and from about 3 percent to about 15 percent of the element by weight and having dispersed therethrough wear-resisting particles, said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.
 20. An article of manufacture comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of an electroless metal alloy consisting of an electroless metal selected from the class consisting of nickel, cobalt, alloys of nickel and cobalt and copper and an element selected from the class consisting of phosphorus and boron, said alloy consisting of from about 85 percent to about 97 percent of the metal and from about 3 percent to about 15 percent of the element by weight and having dispersed therethrough first wear-resisting particles and second wear-resisting particles, all of said particles being essentially insoluble in electroless plating baths and being non-catalytic and inert with respect thereto, said first wear-resisting particles having a hardness substantially greater than that of said electroless metal alloy, said second wear-resisting particles imparting lubricating properties to said coating, all of said particles having dimensions on the order of from about 0.01 micron to about 10 microns and constituting by volume from about 1 percent to about 40 percent of said coating.
 21. An article of manufacture set forth in claim 20, wherein said first wear-resisting particles are silicon carbide particles and said second wear-resisting particles are molybdenum disulfide particles.
 22. An article of manufacturing comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of electroless nickel alloy containing from about 85 percent to 97 percent niCkel and from about 3 to about 15 percent phosphorus by weight, said coating having disbursed there through wear-resisting particles, said particles being essentially insoluble in aqueous solutions and being non-catalytic and inert with respect to the electroless reducing agents for nickel, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating.
 23. An article of manufacturing comprising a workpiece, a wear-resistant coating carried by said workpiece and formed of electroless nickel alloy containing from about 85 percent to 97 percent nickel and from about 3 percent to 15 percent phosphorus by weight and constituting a stable solid characterized by the presence of substantial micro-crystals of nickel phosphide dispersed in a matrix of nickel and having a resulting hardness within the approximate range 1200V.P.N. to 575V.P.N., said wear-resistant coating having a disbursed therethrough wear-resistant particles, said particles being essentially insoluble in aqueous solutions and being non-catalytic and inert with respect to the electroless reducing agents for nickel, said particles having dimensions on the order of from about 0.5 micron to about 25 microns and constituting by volume from about 1 percent to about 40 percent of said coating. 